Automotive exhaust aftertreatment system with doser

ABSTRACT

An exhaust aftertreatment system for use with over-the-road vehicle is disclosed. The exhaust aftertreatment system includes a reducing agent mixer with a mixing can and a doser configured to inject heated and pressurized reducing agent into the mixing can for distribution throughout exhaust gases passed through the mixing can.

BACKGROUND

The present disclosure relates to exhaust aftertreatment systems forautomotive applications, and particularly to mixing devices included inexhaust aftertreatment systems. More particularly, the presentdisclosure relates to injectors, such as dosers, for injecting reducingagents, such as urea solutions, into exhaust streams to mix with theexhaust stream so that chemical reaction between the reducing agent andexhaust gases reduces Nitrous Oxides (NOx) in the exhaust gas.

SUMMARY

An over-the-road vehicle in accordance with the present disclosureincludes an internal combustion engine that produces exhaust gases andan exhaust aftertreatment system configured to treat the exhaust gasesbefore releasing them into the atmosphere. The exhaust aftertreatmentsystem can include a number of components such as, for example, a dieseloxidation catalyst (DOC), a diesel particulate filter (DPF), a selectivecatalytic reduction unit (SCR), and reducing agent mixer.

The reducing agent mixer includes a mixing can defining at least aportion of an exhaust passageway for receiving a flow of exhaust gasestherein and a doser. The doser is mounted to the mixing can andconfigured to inject a reducing agent through an injection apertureformed in the mixing can.

The doser includes a doser body in which reducing agent is conditionedbefore injection into an exhaust stream, a doser inlet coupled to thedoser body, and a doser outlet coupled to the doser body. The doser bodydefines a chamber and may house at least one heater to heat reducingagent and thereby increase a pressure within the chamber. The doserinlet defines an inlet passageway that opens into the chamber to admitreducing agent from an associated reducing agent tank. The doser outletdefines an outlet passageway that opens from the chamber into theexhaust passageway of the mixing can. The doser outlet includes anoutlet valve that blocks or allows flow through the outlet passageway.

Additional features of the present disclosure will become apparent tothose skilled in the art upon consideration of illustrative embodimentsexemplifying the best mode of carrying out the disclosure as presentlyperceived.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The detailed description particularly refers to the accompanying figuresin which:

FIG. 1 is perspective view of an over-the-road automotive vehicleincluding an internal combustion engine and an exhaust aftertreatmentsystem with a doser configured to deliver a reducing agent into engineexhaust gases to treat the exhaust gases before the exhaust gases aredischarged into atmosphere;

FIG. 2 is a cross-sectional and diagrammatic view of a first embodimentof a doser in accordance with the present disclosure showing that thedoser includes (i) a doser body defining a chamber and (ii) an orificeplate located upstream of the chamber with an orifice aperture sized toadmit reducing agent into the chamber and limit reducing agent fromflowing back out of the chamber;

FIG. 2A is a cross-sectional and diagrammatic view of a secondembodiment of a doser in accordance with the present disclosure showingthat the doser includes a doser body defining a chamber and a connectorrod extending between an inlet valve and an exit valve to cause theinlet valve and the exit valve to move in unison as pressure changeswithin the chamber;

FIG. 3 is a cross-sectional and diagrammatic view of a third embodimentof a doser in accordance with the present disclosure including a doserbody, a doser inlet coupled to a side wall of the doser body, and adoser outlet coupled to a bottom wall of the doser body;

FIG. 4 is a cross-sectional and diagrammatic view of a fourth embodimentof a doser in accordance with the present disclosure including a doserbody, a doser inlet coupled to a bottom wall of the doser body, and adoser outlet coupled to the bottom wall of the doser body;

FIG. 5 is a side elevation view of a portion of an exhaustaftertreatment system showing a reducing agent mixer with a dosermounted to a mixer can;

FIG. 6 is a side elevation view of a portion of another exhaustaftertreatment system including a doser mounted to an exhaust conduitand a second doser downstream of the doser;

FIG. 7 is a side elevation view of a portion of another exhaustaftertreatment system including a doser mounted to an exhaust conduitand a second doser downstream of the doser;

FIG. 8 is perspective view of another automotive vehicle including aninternal combustion engine and an exhaust aftertreatment system with anupstream reducing agent mixer located within an engine compartment ofthe vehicle and a downstream reducing agent mixer;

FIG. 9 is a side elevation view of a portion of the exhaustaftertreatment system from FIG. 8 showing a doser included in theupstream reducing agent mixer and a second doser included the downstreamreducing agent mixer;

FIG. 10 is a side elevation view of a portion of another exhaustaftertreatment system showing a doser included in the upstream reducingagent mixer and a second doser included the downstream reducing agentmixer;

FIG. 11 is a side elevation view of a portion of the exhaustaftertreatment system showing a doser configured to supply reducingagent to both the upstream reducing agent mixer and the downstreamreducing agent mixer;

FIG. 12 is a diagrammatic view of various components and devices thatmay be included in the vehicles of FIGS. 1 and 8 with an exhaustaftertreatment system including a reducing agent tank, a reducing agentpump, a doser, and a heater control unit;

FIG. 13 is a diagrammatic view of the heater control unit of FIG. 12;and

FIG. 14 is a diagrammatic view of various components and devices thatmay be included in the vehicles of FIGS. 1 and 8 with another exhaustaftertreatment system.

DETAILED DESCRIPTION

An illustrative over-the-road vehicle 10 includes an engine 12 anexhaust aftertreatment system 14 in accordance with the presentdisclosure as shown, for example, in FIG. 1. The engine 12 is,illustratively, an internal combustion engine configured to combust fueland discharge exhaust gases that are carried through an exhaustpassageway 16 defined by an exhaust conduit 17, treated by the exhaustaftertreatment system 14, and then released into the atmosphere. Theexhaust aftertreatment system 14 is configured to reduce variouseffluents in the exhaust gases, such as, for example, nitrogen oxides(NOx), before the exhaust gases are released to the atmosphere.

In the illustrative embodiment, the exhaust aftertreatment system 14includes a plurality of exhaust aftertreatment devices such as, forexample, a diesel oxidation catalyst (DOC) 18, a diesel particulatefilter (DPF) 20, and a selective catalytic reduction unit (SCR) 22, anda reducing agent mixer 24. The exhaust gases pass through or by each ofthe aftertreatment devices to remove or reduce different effluents. Thereducing agent mixer 18 is mounted upstream of the SCR and is configuredto inject and mix a reducing agent, illustratively a urea solution, intothe exhaust gases. Chemical reaction of the reducing agent with theexhaust gases occurs in downstream of the reducing agent mixer 24 in theSCR 20 to reduce NOx before the exhaust gases are released in theatmosphere.

The reducing agent mixer 24 includes a mixing can 26 and a doser 28, 228as shown in FIGS. 2 and 2A. The mixing can 26 is coupled fluidly withthe exhaust passageway 16 to receive the exhaust gases flowingtherethrough. The reducing agent is stored on the vehicle 10 in areducing agent tank 30 and is conducted to the doser 28, 228 prior tobeing discharged by the doser 28, 228 into a mixing chamber 32 definedby the mixing can 26. In some embodiments, the doser 28, 228 is aflash-boil doser and the reducing agent is heated by the flash-boildoser prior to being discharged into a mixing chamber 32.

A first embodiment of a doser 28 is shown in FIG. 2 and includes a doserbody 34, a doser inlet 36, and a doser outlet 38. The doser body 34includes a housing 40 that defines a chamber 42 and may include at leastone heater 44 arranged in the chamber 42 to heat reducing agent andthereby increase a pressure within the chamber 42. The doser inlet 36 iscoupled to the doser body 34 and defines an inlet passageway 46 thatopens into the chamber 42 to admit reducing agent from the reducingagent tank 30. The doser outlet 38 is coupled to the doser body 34 anddefines an outlet passageway 48 that opens from the chamber 42 into themixing chamber 32 of the mixing can 26 and, hence, the exhaustpassageway 16.

The doser inlet 36 includes an inlet tube 50 defining the inletpassageway 46 and an orifice plate 52 coupled to the inlet tube 50within the inlet passageway 46 as shown in FIG. 2. The orifice plate 52is arranged in the inlet tube 50 to restrict flow through the inletpassageway 46 is formed to include an orifice aperture 54 for admittingreducing agent into the chamber 42 from the reducing agent tank 30. Theinlet passageway 46 has a first cross-sectional area while the orificeaperture 54 has a second cross-sectional area that is smaller than thefirst cross-sectional area.

The orifice aperture 54 is sized to admit reducing agent through theorifice plate 52 and into the chamber 42 when a pressure within thechamber 42 is below the predetermined pressure. The orifice aperture 54is also sized to limit reducing agent from flowing from the chamber 42back through the orifice aperture 54 away from the chamber 42 when thepressure within the chamber 42 is at or above the predeterminedpressure.

The doser outlet 38 includes an outlet tube 56 defining the outletpassageway 48 and an outlet valve 58. In some embodiments, the outletvalve 58 is pressure-activated such that it blocks or allows flowthrough the outlet passageway 48 in response to the pressure within thechamber 42 as shown in FIG. 2. The outlet valve 58 may be configured tomove in response to a pressure change within the chamber 42. An exampleof a doser with a valve portion that moves in response to pressurechange is shown and described in U.S. patent application Ser. No.16/376,683, filed on Apr. 5, 2019, which is incorporated by referenceherein in its entirety.

The heater 44, when included within the chamber 42, is configured toheat reducing agent that is admitted through the orifice aperture 54.The pressure of the reducing agent in the chamber 42 may be increased byheating the reducing agent with the heater 44. As a result of this, thereducing agent may expand due to thermal expansion raising the pressureinside the chamber 42. Due to the pressure of the reducing agent withinthe chamber 42, the reducing agent may be heated to a temperature thatis higher than its normal boiling point. Additionally, the reducingagent may be pre-heated with additional heaters and/or pumps prior toentering the chamber 42. The outlet valve 58 changes to the openposition once the predetermined pressure is reached within the chamber42.

As will be described, the reducing agent inside the chamber 42 can bemonitored by one or more sensors located in the chamber or close to thechamber. The outlet valve 58 may be a mechanical valve that opensautomatically as soon as the predetermined pressure is reached, orcontrolled actively and opened in response to receipt of a sensor signalindicating that the predetermined pressure has been reached.

The doser 28 further includes a cooling system configured to selectivelycool the temperature of select components included in the doser 28 asshown in FIG. 2. The cooling system includes at least one of a firstcooler 62 coupled to an outer surface of the doser inlet 36 and alignedaxially with the orifice plate 52, a second cooler 64 coupled to thedoser body 34, and a third cooler 66 coupled to the doser outlet 38 andaligned axially with the pressure-activated valve 58. Each of thecoolers 62, 64, 66 are illustratively embodied as ducts that hold andcirculate a coolant fluid therethrough to cause heat transfer betweenthe doser 28 and the coolant fluid. The ducts of each cooler 62, 64, 66may be sized according to an amount of thermal heat transfer desired ateach location.

A second embodiment of a doser 228 is shown in FIG. 2A and includes adoser body 234, a doser inlet 236, and a doser outlet 238. The doserbody 234 includes a housing 240 that defines a chamber 242 and mayinclude at least one heater 244 arranged in the chamber 242 to heatreducing agent and thereby increase a pressure within the chamber 242.The doser inlet 236 is coupled to the doser body 234 and defines aninlet passageway 246 that opens into the chamber 242 to admit reducingagent from the reducing agent tank 30. The doser outlet 238 is coupledto the doser body 234 and defines an outlet passageway 248 that opensfrom the chamber 242 into the mixing chamber 232 of the mixing can 26and, hence, the exhaust passageway 16.

The doser outlet 238 includes an outlet tube 256 defining the outletpassageway 248 and an outlet valve 258. The outlet valve 258 may bepressure-activated such that it blocks or allows flow through the outletpassageway 248 in response to the pressure within the chamber 242 asshown in FIG. 2. The outlet valve 258 may move in response to pressurechanging within the chamber 242.

The outlet valve 258 includes an inlet valve 250 that blocks or allowsflow through the inlet passageway 246, an outlet valve 252 that blocksor allows flow through the outlet passageway 248, and a connector rod254 mechanically interconnecting the inlet valve 250 and the outletvalve 252. The connector rod 254 is configured to cause the inlet valve250 to move to a closed position in response to motion of the outletvalve 258 to the opened position and to cause the inlet valve 252 tomove to an opened position in response to motion of the outlet valve 258to the closed position. Reducing agent is admitted into the chamber 242when the inlet valve 250 is in the opened position. Reducing agent isdischarged from the chamber 242 when the outlet valve 252 is in theopened position in response to the pressure within the chamber reachingthe predetermined pressure. The heater 244, when included, is configuredto heat the reducing agent to increase the pressure within the chamber242 in the same way as described above regarding doser 28.

The doser 228 further includes a cooling system configured toselectively cool the temperature of select components included in thedoser 228 as shown in FIG. 2A. The cooling system includes at least oneof a first cooler 262 coupled to an outer surface of the doser inlet 236and aligned axially with the inlet valve 250, a second cooler 264coupled to the doser body 234, and a third cooler 266 coupled to thedoser outlet 238 and aligned axially with the outlet valve 252. Each ofthe coolers 262, 264, 266 are illustratively embodied as ducts that holdand circulate a coolant fluid therethrough to cause heat transferbetween the doser 228 and the coolant fluid. The ducts of each cooler262, 264, 266 may be sized according to an amount of thermal heattransfer desired at each location.

The doser inlet 36 and the doser outlet 38 are generally aligned alongan axis 35 as shown in FIG. 2. However, in other embodiments, the doserinlet 36 and the doser outlet 38 may be misaligned as shown in FIGS. 3and 4.

A third embodiment of a doser 328 is shown in FIG. 3 and includes adoser body 334, a doser inlet 336, and a doser outlet 338. The doser 328is similar to doser 28 and similar reference numbers in the 300 seriesare used in FIG. 3 to denote similar features between doser 28 and doser328. The doser 328 is different from the doser 28 in that the doserinlet 336 is coupled to a side wall 341 of the doser body 334 while thedoser outlet 338 is coupled to a bottom wall 343 of the doser body 334.

A fourth embodiment of a doser 428 is shown in FIG. 4 and includes adoser body 434, a doser inlet 436, and a doser outlet 438. The doser 428is similar to doser 28 and similar reference numbers in the 400 seriesare used in FIG. 4 to denote similar features between doser 28 and doser428. The doser 428 is different from the doser 28 in that the doserinlet 436 and the doser outlet 438 are both coupled to a bottom wall 443of the doser body 434.

Each of the dosers 28, 228, 328, 428 may be used with variousembodiments of exhaust aftertreatment systems as shown in FIGS. 5-11. Asdescribed above, the exhaust aftertreatment system 14 includes aplurality of exhaust aftertreatment devices such as, for example, DOC18, DPF 20, (SCR) 22, and the reducing agent mixer. The dosers 28, 228,328, 428 are mounted to the mixing can 26 of the reducing agent mixer 24to inject the reducing agent into the mixing chamber 32 upstream of theSCR 22. In other embodiments, more than one SCR and/or reducing agent 24may be used as will be described.

A second embodiment of an exhaust after treatment system 514 is shown inFIG. 6. The exhaust aftertreatment system 514 is similar to exhaustaftertreatment system 14 and similar reference numbers in the 500 seriesare used to denote similar features that are common between exhaustaftertreatment system 14 and exhaust aftertreatment system 514 exceptfor the differences described below.

The exhaust aftertreatment system 514 includes a first reducing agentmixer 524 with a doser 528, a first SCR 522, a second reducing agentmixer 570, and a second SCR 572 as shown in FIG. 6. The first reducingagent mixer 524 with the doser 528 is located upstream and spaced apartfrom all of the other aftertreatment devices. The doser 528 may be anyone of dosers 28, 228, 328, 428 described above.

A third embodiment of an exhaust after treatment system 614 is shown inFIG. 7. The exhaust aftertreatment system 614 is similar to exhaustaftertreatment system 514 and similar reference numbers in the 600series are used to denote similar features that are common betweenexhaust aftertreatment system 514 and exhaust aftertreatment system 614except for the differences described below.

The exhaust aftertreatment system 614 includes a first reducing agentmixer 624 with a doser 628, a first SCR 622, a second reducing agentmixer 670, and a second SCR 672 as shown in FIG. 7. The first reducingagent mixer 624 with the doser 628 is located upstream and immediatelyadjacent to the first SCR 622. The doser 628 may be any one of dosers28, 228, 328, 428 described above.

An illustrative automotive vehicle 210 is shown in FIG. 8 with aninternal combustion engine 212 contained within an engine compartment513, a downstream exhaust after treatment system 214, and an upstreamexhaust aftertreatment system 215 spaced apart from the downstreamexhaust aftertreatment system 214. The upstream exhaust aftertreatmentsystem 215 is close-coupled with the engine 214 within the enginecompartment 213. Some examples of exhaust aftertreatment systems with aclose coupled reducing agent mixer in accordance with the presentdisclosure are shown in FIGS. 9-11 and described below.

A fourth embodiment of an exhaust after treatment system 714 is shown inFIG. 9. The exhaust aftertreatment system 714 is similar to exhaustaftertreatment system 614 and similar reference numbers in the 700series are used to denote similar features that are common betweenexhaust aftertreatment system 614 and exhaust aftertreatment system 714except for the differences described below.

The exhaust aftertreatment system 714 includes a first reducing agentmixer 724 with a doser 728, a first SCR 722, a second reducing agentmixer 770, and a second SCR 772 as shown in FIG. 9. The first reducingagent mixer 724 with the doser 728 and the first SCR 722 areclose-coupled with the engine 212 while the second reducing agent mixer770 and the second SCR 772 are located downstream from the doser 728 andthe first SCR 722. The doser 724 is located immediately adjacent to thefirst SCR 722. The doser 728 may be any one of dosers 28, 228, 328, 428described above.

A fifth embodiment of an exhaust after treatment system 814 is shown inFIG. 10. The exhaust aftertreatment system 814 is similar to exhaustaftertreatment system 714 and similar reference numbers in the 800series are used to denote similar features that are common betweenexhaust aftertreatment system 714 and exhaust aftertreatment system 814except for the differences described below.

The exhaust aftertreatment system 814 includes a first reducing agentmixer 824 with a doser 828, a first SCR 822, a second reducing agentmixer 870, and a second SCR 872 as shown in FIG. 10. The first reducingagent mixer 824 with the doser 828 and the first SCR 822 areclose-coupled with the engine 212 while the second reducing agent mixer870 and the second SCR 872 are located downstream from the doser 828 andthe first SCR 822. Additionally, the doser 828 is spaced apart upstreamfrom the first SCR 822. The doser 828 may be any one of dosers 28, 228,328, 428 described above.

A sixth embodiment of an exhaust after treatment system 914 is shown inFIG. 11. The exhaust aftertreatment system 914 is similar to exhaustaftertreatment system 714 and similar reference numbers in the 900series are used to denote similar features that are common betweenexhaust aftertreatment system 714 and exhaust aftertreatment system 914except for the differences described below.

The exhaust aftertreatment system 914 includes a first reducing agentmixer 924, a first SCR 922, a second reducing agent mixer 970, and asecond SCR 972 as shown in FIG. 10. The first reducing agent mixer 924and the first SCR 922 are close-coupled with the engine 212 while thesecond reducing agent mixer 970 and the second SCR 972 are locateddownstream from the first reducing agent mixer 924 and the first SCR922. A conduit 974 extends from the exhaust passageway 916 to each ofthe reducing agent mixers 924, 970. A doser 928 is coupled to theconduit 974 and spaced apart exhaust passageway 916. The doser 928 isconfigured to inject reducing agent into the conduit 974 which isconducted through the conduit 974 to both reducing agent mixers 924,970. Corresponding check valves 976 are positioned upstream of eachreducing agent mixer 924, 970 to regulate an amount of reducing agentdelivered to each. The doser 928 may be any one of dosers 28, 228, 328,428 described above.

Referring now to FIGS. 12-14, a diagrammatic view of the exhaustaftertreatment system 14 is shown with other components or unitsassociated with the exhaust aftertreatment system 14. The exhaustaftertreatment system 14 includes the doser 28, the reducing agent tank30, a reducing agent pump 80 and a heater control unit (HCU) 82 as shownin FIG. 12. A plurality of sensors 84 are coupled to the reducing agenttank 30, the reducing agent pump 80 and the doser 28. The sensors 84 areconfigured to measure properties of reducing agent associatedwith/retained in each component to which they are coupled and outputsignals to an electronic control unit (ECU) 86. For example, the sensors84 may measure temperature, pressure, flow rate, fluid level, and/orother properties at the locations shown. The ECU 86 receives the signalsand includes all of the functionality necessary to operate each of thecomponents associated with the exhaust aftertreatment system 14 inresponse to the sensor signals output from one or more of the sensors84.

The reducing agent pump 80 is configured to displace reducing agentstored in the reducing agent tank 30 to the doser 28. Unused reducingagent may be returned to the reducing agent tank 30. A pre-heater 88 iscoupled to the reducing agent pump 80 and is configured to selectivelyheat the reducing agent displaced from the reducing agent tank 30 beforethe reducing agent reaches the doser 28. Engine coolant 90 may be routedto the reducing agent tank 30 to cool returned, pre-heated reducingagent. An additional pre-heater 89 is coupled to a line 100 used totransfer the displaced reducing agent from the reducing agent pump 80 tothe doser 28. In the illustrative embodiment shown in FIG. 12, each ofthe heaters 44, 88, 89 are electric heaters.

The ECU 86 is coupled with a controlled area network (CAN) 92 thatallows each of the components associated with the exhaust aftertreatmentsystem 14 to communicate with one another during operation. The ECU 86is also coupled to the HCU 82 which is used to control the function ofeach of the heaters 44, 88, 89 depending on the signals output from eachof the sensors 84 and received by the ECU 86.

The HCU 92 includes a microprocessor 102, at least one p-channelfield-effect transistor (P-FET) 104, a watchdog timer 106 coupled to theP-FET 104, and a plurality of n-channel field-effect transistors (N-FET)108 as shown in FIG. 13. The microprocessor 102 is coupled to the CAN 92to receive instructions from the ECU 86 that, when executed by themicroprocessor 102, cause the P-FET 104 and each of the N-FETs 108 tooutput selectively power from a battery 110 to each of the heaters 44,88, 89 in response to the signals provided by the sensors 84 to the ECU86. Accordingly, each of the heaters 44, 88, 89 may be controlledindividually to apply increased or reduced thermal energy to theircorresponding components. The watchdog timer 106 is used to enable theP-FET 104 as a main relay. Any number of heaters and associated N-FETs108 may be used in the exhaust aftertreatment system 14. Each of theheaters are grounded at 112.

In other embodiments, different types of heaters may be used andassociated with the various components of the exhaust aftertreatmentsystem 14. For example, a heater 1044 may be embodied as an exhaustshroud that diverts hot exhaust gases from the exhaust passageway 16 tothe doser 28 as shown in FIG. 14. The heater 1044 is fluidly coupled tothe exhaust passageway 16 to receive hot exhaust gases that driveheating of the reducing agent resident in the chamber 42. The heatercontrol unit 92 is configured to adjust at least one valve 114 tomodulate the flow of hot exhaust gases from the exhaust passageway 16 tothe heater 1044 in order to manipulate operation of the heater 1044 ofthe doser 28.

In illustrative embodiments, the inlet valve 250 is used to let cold DEF(reducing agent) flow into the chamber and outlet valve 252 is used tolet cold/hot DEF flow out of the chamber towards the nozzle. In thisillustrative disclosure, one single valve 258 replaces separate inletand outlet valves. This single valve 258 will perform the same functionswhich otherwise will be performed by separate inlet and outlet valve. Inanother embodiment, inlet valve is replaced by an orifice 52, 54. Theorifice 52, 54 is sized in such a way that even in an increased pressureinside the heating chamber 42 situation, DEF solution inside chamberdoesn't backflow.

In illustrative embodiments, the heater 44, 244 within the heatingchamber 42, 242 heats the DEF to 160 C. At this temperature the DEF isat the saturated vapor pressure. At this temperature range DEFcavitation could occur. Another potential problem may be the temperaturelimits of the mechatronics of the injector assembly 28, 228 (i.e.plastic housing 40 and coil 44). To help mitigate these issues, acooling system is included. The cooling system includes plumbing 62, 64,66, 262, 264, 266 (metal tubing made of stainless steel, aluminum, orsuitable DEF resistant material) in strategic areas to selectively coolthese areas below the cavitation threshold and the mechatroniccomponents.

In illustrative embodiments, the doser 28, 228 can be used as a seconddoser under floor or in close coupled position closer to the engine 12,212 with a low temperature SCR 22. The doser may be easy to install intoan inpipe mixing or a compact mixing location. The doser 28, 228 can beused with the main underfloor SCR. The doser 28, 228 can be used to dosehot or at ambient temperatures. The same doser 28, 228 can also be usedfor both the low temperature SCR and the main underfloor SCR.

In some embodiments, the electrical heaters 44 may be replaced with heatfrom the exhaust (i.e. heater 1044). There is a valve 114 to control theexhaust flow through the exhaust shroud 1044. The shroud 1044 surroundsthe doser body 34, 234 allowing the exhaust gas to heat the doser 28,228.

The following numbered clauses include embodiments that are contemplatedand non-limiting:

Clause 1. A reducing agent mixer for use in an exhaust aftertreatmentsystem for an over-the-road vehicle, the reducing agent mixer comprisinga mixing can defining at least a portion of an exhaust passageway forreceiving a flow of exhaust gases therein.

Clause 2. The reducing agent mixer of clause 1, any other suitableclause, or any combination of suitable clauses, further comprising adoser mounted to the mixing can and configured to inject a reducingagent through an injection aperture formed in the mixing can.

Clause 3. The reducing agent mixer of clause 2, any other suitableclause, or any combination of suitable clauses, wherein the doserincluding (i) a doser body that defines a chamber.

Clause 4. The reducing agent mixer of clause 3, any other suitableclause, or any combination of suitable clauses, wherein the doserfurther includes (ii) a doser inlet coupled to the doser body thatdefines an inlet passageway that opens into the chamber to admitreducing agent from an associated reducing agent tank.

Clause 5. The reducing agent mixer of clause 4, any other suitableclause, or any combination of suitable clauses, wherein the doserfurther includes (iii) a doser outlet coupled to the doser body thatdefines an outlet passageway that opens from the flash-boil chamber intothe exhaust passageway of the mixing can.

Clause 6. The reducing agent mixer of clause 5, any other suitableclause, or any combination of suitable clauses, wherein the doser outletincludes an outlet valve that blocks or allows flow through the outletpassageway.

Clause 7. The reducing agent mixer of clause 6, any other suitableclause, or any combination of suitable clauses, wherein the outlet valveis configured to discharge the reducing agent from the chamber throughthe outlet passageway and into the exhaust passageway for mixing withthe exhaust gases therein.

Clause 8. The reducing agent mixer of clause 7, any other suitableclause, or any combination of suitable clauses, wherein the doser inletincludes an inlet tube defining the inlet passageway having a firstcross-sectional area and an orifice plate that defines an orificeaperture therethrough having a second cross-sectional area that issmaller than the first cross-sectional area, and wherein the orificeplate is arranged in the inlet tube to restrict flow through the inletpassageway.

Clause 9. The reducing agent mixer of clause 8, any other suitableclause, or any combination of suitable clauses, wherein the orificeaperture is sized to admit reducing agent through the orifice plate andinto the chamber when the pressure within the chamber is below thepredetermined pressure and to limit reducing agent from flowing from thechamber back through the orifice aperture away from the chamber when thepressure within the chamber is at or above the predetermined pressure.

Clause 10. The reducing agent mixer of clause 8, any other suitableclause, or any combination of suitable clauses, the doser furtherincludes (iv) a cooling system configured to selectively cool thetemperature of components included in the doser.

Clause 11. The reducing agent mixer of clause 10, any other suitableclause, or any combination of suitable clauses, wherein the coolingsystem includes at least one of a first cooler coupled to an outersurface of the doser inlet and aligned axially with the orifice plate.

Clause 12. The reducing agent mixer of clause 11, any other suitableclause, or any combination of suitable clauses, wherein the coolingsystem further includes a second cooler coupled to the doser body.

Clause 13. The reducing agent mixer of clause 12, any other suitableclause, or any combination of suitable clauses, wherein the coolingsystem includes a third cooler coupled to the doser outlet and alignedaxially with the pressure-activated valve.

Clause 14. The reducing agent mixer of clause 7, any other suitableclause, or any combination of suitable clauses, wherein the outlet valveincludes an inlet valve that blocks or allows flow through the inletpassageway and a connector rod mechanically interconnecting the inletvalve and the outlet valve, the connector rod configured to cause theinlet valve to move to a closed position in response to motion of theoutlet valve to the opened position and to cause the inlet valve to moveto an opened position in response to motion of the outlet valve to theclosed position.

Clause 15. The reducing agent mixer of clause 14, any other suitableclause, or any combination of suitable clauses, wherein the doserfurther includes (iv) a cooling system configured to selectively coolthe temperature of components included in the doser, the cooling systemincluding at least one of a first cooler coupled to an outer surface ofthe doser inlet and aligned axially with the orifice plate, a secondcooler coupled to the doser body, and a third cooler coupled to thedoser outlet and aligned axially with the pressure-activated valve.

Clause 16. An exhaust after treatment system comprising an exhaustconduit defining an exhaust passageway for receiving a flow of exhaustgases therein.

Clause 17. The exhaust after treatment system of clause 16, any othersuitable clause, or any combination of suitable clauses furthercomprising a first reducing agent mixer coupled fluidly with the exhaustconduit and configured to receive the exhaust gases and inject areducing agent into the exhaust gases.

Clause 18. The exhaust after treatment system of clause 17, any othersuitable clause, or any combination of suitable clauses, wherein thereducing agent mixer includes a mixing can defining at least a portionof the exhaust passageway for receiving the exhaust gases therein.

Clause 19. The exhaust after treatment system of clause 18, any othersuitable clause, or any combination of suitable clauses, wherein thereducing agent mixer further includes a doser mounted to the mixing canand configured to inject a reducing agent through an injection apertureformed in the mixing can.

Clause 20. The exhaust after treatment system of clause 19, any othersuitable clause, or any combination of suitable clauses, wherein thedoser includes (i) a doser body that defines a chamber.

Clause 21. The exhaust after treatment system of clause 20, any othersuitable clause, or any combination of suitable clauses, wherein thedoser further includes (ii) a doser inlet coupled to the doser body thatdefines an inlet passageway that opens into the chamber to admitreducing agent from an associated reducing agent tank.

Clause 22. The exhaust after treatment system of clause 21, any othersuitable clause, or any combination of suitable clauses, wherein thedoser further includes (iii) a doser outlet coupled to the doser bodythat defines an outlet passageway that opens from the chamber into theexhaust passageway of the mixing can.

Clause 23. The exhaust after treatment system of clause 22, any othersuitable clause, or any combination of suitable clauses, wherein thedoser outlet includes an outlet valve that blocks or allows flow throughthe outlet passageway.

Clause 24. The exhaust after treatment system of clause 23, any othersuitable clause, or any combination of suitable clauses, wherein theoutlet valve is configured to discharge the reducing agent from thechamber through the outlet passageway and into the exhaust passagewayfor mixing with the exhaust gases therein.

Clause 25. The system of clause 24, any other suitable clause, or anycombination of suitable clauses, further comprising a second reducingagent mixer coupled to the exhaust conduit downstream of the firstreducing agent mixer, the second reducing agent mixer including a secondmixing can defining at least a portion of the exhaust passageway forreceiving the exhaust gases therein and a secondary doser mounted to thesecond mixing can, wherein the secondary doser is configured to injectreducing agent through a second injection aperture formed in the secondmixing can.

Clause 26. The system of clause 25, any other suitable clause, or anycombination of suitable clauses, further comprising a first selectivecatalytic reduction unit mounted to the exhaust conduit downstream ofthe first reducing agent mixer and a second selective catalyticreduction unit mounted to the exhaust conduit downstream of the secondreducing agent mixer.

Clause 27. The system of clause 26, any other suitable clause, or anycombination of suitable clauses, wherein the first selective catalyticreduction unit is spaced apart from the first reducing agent mixer andthe second selective catalytic reduction unit is positioned immediatelydownstream of the second reducing agent mixer.

Clause 28. The system of clause 26, any other suitable clause, or anycombination of suitable clauses, wherein the first reducing agent mixerand the first selective catalytic reduction unit are close-coupledrelative to a source of the exhaust gases and the second reducing agentmixer.

Clause 29. An over the road vehicle, the vehicle comprising an internalcombustion engine configured to produce a flow of exhaust gases that areconducted through an exhaust passageway defined by an exhaust conduit.

Clause 30. The over the road vehicle of clause 29, any other suitableclause, or any combination of suitable clauses, further comprising anexhaust aftertreatment system comprising a reducing agent tank formed toinclude an internal region storing a reducing agent therein.

Clause 31. The over the road vehicle of clause 29, any other suitableclause, or any combination of suitable clauses, wherein the exhaustaftertreatment system further includes a reducing agent pump configuredto displace reducing agent from the reducing agent tank.

Clause 32. The over the road vehicle of clause 31, any other suitableclause, or any combination of suitable clauses, wherein the exhaustaftertreatment system further includes a doser mounted to the mixing canand configured to inject a reducing agent through an injection apertureformed in the mixing can.

Clause 33. The over the road vehicle of clause 32, any other suitableclause, or any combination of suitable clauses, wherein the doserincludes (i) a doser body that defines a chamber.

Clause 34. The over the road vehicle of clause 33, any other suitableclause, or any combination of suitable clauses, wherein the doserfurther includes (ii) a doser inlet coupled to the doser body thatdefines an inlet passageway that opens into the chamber to admitreducing agent from an associated reducing agent tank.

Clause 35. The over the road vehicle of clause 34, any other suitableclause, or any combination of suitable clauses, wherein the doserfurther includes (iii) a doser outlet coupled to the doser body thatdefines an outlet passageway that opens from the chamber into theexhaust passageway of the mixing can, wherein the doser outlet includesan outlet valve that blocks or allows flow through the outletpassageway.

Clause 36. The over the road vehicle of clause 35, any other suitableclause, or any combination of suitable clauses, wherein the outlet valveis configured to discharge the reducing agent from the chamber throughthe outlet passageway and into the exhaust passageway for mixing withthe exhaust gases therein.

Clause 37. The over the road vehicle of clause 36, any other suitableclause, or any combination of suitable clauses, wherein the exhaustaftertreatment system further includes a reducing agent sensorconfigured to detect a parameter associated with reducing agent withinthe exhaust aftertreatment system.

Clause 38. The over the road vehicle of clause 37, any other suitableclause, or any combination of suitable clauses, wherein the exhaustaftertreatment system further includes, a heater control unit incommunication with the reducing agent sensor and configured toselectively operate a heater based on signals received from the reducingagent sensor.

Clause 39. The over-the-road vehicle of clause 38, any other suitableclause, or any combination of suitable clauses, wherein the exhaustaftertreatment system includes a pre-heater configured to increase thetemperature of reducing agent present in at least one of the reducingagent tank and the reducing agent pump, and wherein the heater controlunit is configured to manipulate operation of the pre-heater based onsignals received from the reducing agent sensor.

Clause 40. The over-the-road vehicle of clause 38, any other suitableclause, or any combination of suitable clauses, wherein the heater isfluidly coupled to the exhaust passageway to receive hot exhaust gasesthat drive heating of the reducing agent resident in the chamber, andwherein the heater control unit is configured to adjust at least onevalve to modulate the flow of hot exhaust gases from the exhaustpassageway to the heater in order to manipulate operation of the heaterof the doser.

Clause 41. The over-the-road vehicle of clause 38, any other suitableclause, or any combination of suitable clauses, wherein the heater iselectrically coupled to a power source that drives heating of thereducing agent resident in the chamber, and wherein the heater controlunit is configured to adjust the electrical current applied to theheater in order to manipulate operation of the heater.

The invention claimed is:
 1. An exhaust aftertreatment systemcomprising: an exhaust conduit defining an exhaust passageway forreceiving a flow of exhaust gases therein, and a first reducing agentmixer coupled fluidly with the exhaust conduit and configured to receivethe exhaust gases and inject a reducing agent into the exhaust gases,the reducing agent mixer including: a mixing can defining at least afirst portion of the exhaust passageway for receiving the exhaust gasestherein, a doser mounted to the mixing can and configured to inject areducing agent through an injection aperture formed in the mixing can,the doser being configured to heat the reducing agent above a saturatedvapor pressure of the reducing agent, and a second reducing agent mixercoupled to the exhaust conduit downstream of the first reducing agentmixer, the second reducing agent mixer including a second mixing candefining at least a second portion of the exhaust passageway forreceiving the exhaust gases therein and a secondary doser mounted to thesecond mixing can, wherein the secondary doser is configured to injectreducing agent through a second injection aperture formed in the secondmixing can.
 2. The system of claim 1, further comprising a firstselective catalytic reduction unit mounted to the exhaust conduitdownstream of the first reducing agent mixer and a second selectivecatalytic reduction unit mounted to the exhaust conduit downstream ofthe second reducing agent mixer.
 3. The system of claim 2, wherein thefirst selective catalytic reduction unit is spaced apart from the firstreducing agent mixer and the second selective catalytic reduction unitis positioned immediately downstream of the second reducing agent mixer.4. The system of claim 2, wherein the first reducing agent mixer and thefirst selective catalytic reduction unit are close-coupled relative to asource of the exhaust gases and the second reducing agent mixer.
 5. Anover the road vehicle, the vehicle comprising: an internal combustionengine configured to produce a flow of exhaust gases that are conductedthrough an exhaust passageway defined by an exhaust conduit, and anexhaust aftertreatment system comprising a reducing agent tank formed toinclude an internal region storing a reducing agent therein, a reducingagent pump configured to displace reducing agent from the reducing agenttank, a doser mounted to a mixing can and configured to inject areducing agent through an injection aperture formed in the mixing can,the doser being configured to heat the reducing agent above a saturatedvapor pressure of the reducing agent, a reducing agent sensor configuredto detect a parameter associated with the reducing agent within theexhaust aftertreatment system, and a heater control unit incommunication with the reducing agent sensor and configured toselectively operate a heater based on signals received from the reducingagent sensor, wherein the heater is fluidly coupled to the exhaustpassageway to receive hot exhaust gases that drive heating of thereducing agent resident in a chamber, and wherein the heater controlunit is configured to adjust at least one valve to modulate the flow ofhot exhaust gases from the exhaust passageway to the heater in order tomanipulate operation of the heater.
 6. The over-the-road vehicle ofclaim 5, wherein the exhaust aftertreatment system includes a pre-heaterconfigured to increase the temperature of reducing agent present in atleast one of the reducing agent tank and the reducing agent pump, andwherein the heater control unit is configured to manipulate operation ofthe pre-heater based on signals received from the reducing agent sensor.7. The over the road vehicle of claim 5, wherein the doser is operableto inject the reducing agent through the injection aperture in both aheated mode and a non-heated mode.
 8. The over the road vehicle of claim7, wherein the doser is configured to change between the heated mode andthe non-heated mode based on engine or aftertreament system parameters.9. The over the road vehicle of claim 8, wherein the engine oraftertreatment parameters includes at least one of exhaust massflowrate, exhaust temperature, engine revolutions per minute, and engineload.
 10. The over the road vehicle of claim 7, wherein the doserincludes a cooling system configured to selectively cool the temperatureof components included in the doser.
 11. The over the road vehicle ofclaim 10, wherein the doser further includes (iv) a cooling systemconfigured to selectively cool the temperature of components included inthe doser, the cooling system including at least one of a first coolercoupled to an outer surface of a doser inlet and aligned axially withthe orifice plate, a second cooler coupled to a doser body, and a thirdcooler coupled to a doser outlet and aligned axially with apressure-activated valve.